Mobile and Ubiquitous Computing: Android Programming (part 3)

Transcription

1 Mobile and Ubiquitous Computing: Android Programming (part 3) Master studies, Winter 2015/2016 Dr Veljko Pejović Based on Programming Handheld Systems, Adam Porter, University of Maryland Examples from: Smartphone Programming Andrew Campbell, Dartmouth College

2 Android Security Applications are sandboxed Each app has its user ID and group ID that is unique for the device Allocated resources for the user ID Only the most basic functionalities are available to an application, other functionalities have to be explicitly asked for

3 Permissions An app requests permissions to access: User data (e.g. contacts) Some cost-sensitive APIs (e.g. send SMS) Some system resources (e.g. camera) Permissions are declared in AndroidManifest.xml Predefined Strings from Manifest.permission <user-permission> in Manifest indicates a request: <uses-permission android:name= android.permission.access_fine_location />

4 Permissions Types Normal permissions FLASHLIGHT, VIBRATE, BLUETOOTH, etc. Dangerous permissions READ_CONTACTS, SEND_SMS, ACCESS_COARSE_LOCATION, WRITE_EXTERNAL_CONTACTS, etc. The OS will explicitly ask the user to grant access for dangerous permissions

5 Handling Permissions Prior to Marshmallow (API 23): Users must accept permissions before the app starts Marshmallow (API 23): Permissions can also be granted at the runtime, when the functionality is about to be used Ask straight away, educate up front, ask in context, educate in context See a short explanation by Google devs:

6 Custom Permissions Define your own permission if the app performs a privileged/dangerous function, and you don t want just any app to be able to launch yours In AndroidManifest.XML under <permission> Example: <permission android:name="com.testpackage.mypermission" android:label="my_permission android:protectionlevel="dangerous /> Any app that wants to launch yours must request com.testpackage.mypermission

7 Component Permissions Permissions can be defined for individual components restricting which other component can call them Activities Which components can call startactivity() Services Which components can start or bind to a Service BroadcastReceivers Which components can receive and send broadcasts ContentProviders Which components can read and write content provider data

8 Permissions Design Do not request permissions unless you really need them E.g. do you need to write data to an external storage (file) or can you keep the information in SharedPrefs? Show immediate benefit of granting a permission E.g. your ToDo list app requires location info show the user how she can make location-based reminders Use Intents to call other apps in case you don t need to handle the functionality within your app: E.g. call a camera app, rather than requesting the camera permission for your app

9 Google Map in Android Provided by Google Play Services Add to Android Studio via SDK Manager Needs maps API key Obtain your apps short signature (SHA-1) Create an API project in the Google API console Generate the maps API key Put it in your app s AndroidManifest.xml <meta-data android:name="com.google.android.geo.api_key" android:value=your_key/>

10 Google Map in Android Android Studio automates this via New->Google Maps Activity Google maps require permissions <uses-permission android:name= "android.permission.internet" /> <uses-permission android:name= "android.permission.access_network_state" /> <uses-permission android:name= "android.permission.write_external_storage" /> <uses-permission android:name= "com.google.android.providers.gsf.permission.read_gservices" />

11 Google Map in Android Map is basically a Fragment com.google.android.gms.maps.supportmapfragment Note: you need Internet connectivity to show it Operations: Set map type (satellite, normal, hybrid, terrain) Capture onclick events Add markers, capture onmarkerclick events

12 Google Map in Android You can do much more: Draw on the map Different layers Get address Show user s location Get directions Show 3D view (in selected areas) Try at home:

13 Services Activities run on the main thread UI thread Processing-heavy functions on the main thread impact the responsiveness Services run on a separate background thread Outside UI, for long-running operations Services can be created: Explicitly using Context.startService() Implicitly, if not already running, when a client requests connection to a Service via Context.bindService()

14 Multiple startservice calls do not nest you only have one service; however, onstartcommand() will be called repeatedly Service will be stopped only once with Context.stopService() or stopself() Services

15 Services Bound Services started through binding do not call onstartcommand() Return IBinder object from onbind(intent) so that connected clients can call the Service The service remains running as long as the connection is established

16 BroadcastReceiver Receive events announced by other components Events announced via Intents Not the same Intent as the one starting an Activity: this one remains in the background Events can be announced within your app or publicly to every app on the phone Announce via sendbroadcast() Events captured if the receiver is registered: onreceiverregistered() and then onreceive()

17 Notifications Allows the app to initiate contact with the user Shown in the Status Bar (Notification Bar) Custom icons Alerts: sound, vibration, LED flashing Notification drawer NotificationManager

18 Service, Notification, BroadcastReceiver Example

19 Android UI UI is usually provided via Activities and Fragments setcontentview(view v) View System from the Application Framework

20 View View is the main class on which the View System operates Responsible for drawing itself and handling events From View we derive other UI objects: Button, EditText fields, MapView, RadioButton, WebView, LinearLayout, etc. View and its derived classes can be instantiated: through the XML code in Resources through Java source code

21 View Example Button: In an XML layout: <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_gravity="center_horizontal /> The benefit of using XML separate functionality from presentation (think MVC)

22 View Example Button: In Activity through Java code : final Button button = (Button) findviewbyid(r.id.register_button); button.setonclicklistener(new View.OnClickListener() public void onclick(view view) { // Do something, i.e. register a user } }); Yet, accessing through Java brings a lot of flexibility

23 Other View Examples TextView EditText CheckBox SeekBar Switch CalendarView

24 Other View Examples AdapterViews Separation between the data (model) and children views Adapter manages the data and provides it to the views Example: ListView Displays a scrollable list of items, where the list is populated through an Adapter ArrayAdapter is the most common, but you can implement your own Adapter as well Convenience classes: ListActivity and ListFragment

25 View Properties View parameters Text, padding, layout, colour, etc. Layout: WRAP_CONTENT vs MATCH_PARENT android:layout_width="wrap_content android:layout_height="wrap_content android:layout_gravity="center_horizontal Also accessible through Java: change visibility, modify text, get checked state, etc.

26 View Events Stem from user interaction and lifecycle changes Listeners used for handling View events OnClickListener.onClick() capture View clicked event OnLongClickListener.onLongClick() capture View clicked and held for some time OnTouchListener.onTouch() capture View touched And quite a few more Capturing gestures: GestureDetector.OnGestureListener

27 View Events Example Capture onclick event private OnClickListener mlistener = new OnClickListener() { public void onclick(view v) { // do something when the button is clicked } }; protected void oncreate(bundle savedvalues) {... // Capture our button from layout Button button = (Button)findViewById(R.id.button); // Register the onclick listener with the implementation above button.setonclicklistener(mlistener);... }

28 Displaying Views Views are organised in a tree with the root View containing all the others UI Hierarchy Viewer in Android Studio allows you to examine the hierarchy of your views Displaying Views includes Measuring each of the elements (calling onmeasure()) Aligning the children (calling onlayout()) Rendering the view (ondraw())

29 Grouping Views ViewGroup An invisible View that contains other Views Used for grouping and organizing views Example: RadioGroup, TimePicker, Spinner Layout A ViewGroup that defines a structure for the Views it contains

30 Layouts LinearLayout Child views arranged in a single horizontal or vertical row RelativeLayout Child views are positioned relative to each other and to parent view TableLayout Child views arranged into rows and columns But also other layouts: FrameLayout, GridLayout, TabLayout, etc.

31 Menus Formalised in Android to provide consistent user experience across applications Activities support menus: Add items to a menu Handle onclick events for the menu Menu types: Options menu Context menu Popup menu

32 Options Menu Primary menu where actions such as compose new , settings and similar are added Define in an XML file, put in res/menu <?xml version="1.0" encoding="utf-8"?> <menu xmlns:android=" <item android:showasaction="ifroom"/> <item /> </menu>

33 Options Menu Inflate in Activity- override public boolean oncreateoptionsmenu(menu menu) { MenuInflater inflater = getmenuinflater(); inflater.inflate(r.menu.game_menu, menu); return true; } Handle onclick events Note: Fragments have their own public boolean onoptionsitemselected(menuitem item) { switch (item.getitemid()) { case R.id.new_game: newgame(); return true; case R.id.help: showhelp(); return true;

34 Context Menu Options that affect the selected item in the context of the current UI frame Floating context menu Contextual action mode

35 Context Menu Define your menu in res/menu as an XML file Register a View for a context menu Button btn = (Button) findviewbyid(r.id.btn); registerforcontextmenu(btn); Inflate context public void oncreatecontextmenu(contextmenu menu, View v, ContextMenuInfo menuinfo) { super.oncreatecontextmenu(menu, v, menuinfo); MenuInflater inflater = getmenuinflater(); inflater.inflate(r.menu.context_menu, menu);} Capture on item selected events public boolean oncontextitemselected(menuitem item)

36 Toolbar Allows quick access to frequently used operations Title, logo, navigation, action menu Similar to the application bar in desktop apps Toolbar - Introduced in API 21 (Lollipop) to replace ActionBar introduced in API 11 Toolbar is more general than ActionBar (which is closely tied to an Activity), as it can be placed anywhere within the view hierarchy

37 Use Toolbar as ActionBar dependencies { compile filetree(dir: 'libs', include: ['*.jar']) compile "com.android.support:appcompat-v7:21.0.+" } Gradle <android.support.v7.widget.toolbar android:id="@+id/toolbar android:layout_width="match_parent android:layout_height="wrap_content"> </android.support.v7.widget.toolbar> import android.support.v7.app.appcompatactivity; import android.support.v7.widget.toolbar; Layout XML Activity Java public class MyActivity extends protected void oncreate(bundle savedinstancestate) { super.oncreate(savedinstancestate); setcontentview(r.layout.activity_my); Toolbar toolbar = (Toolbar) findviewbyid(r.id.toolbar); setsupportactionbar(toolbar); } }